Black Scoters in the Old World have food habits similar to those of North 

 American birds and often feed largely on molluscs. In Iceland, young birds ate 

 mostly aquatic insects and seeds; females mostly ate chironomid larvae and a few 

 adult males ate mostly fish eggs and some chironomid larvae (Bengtson 1971). A 

 number of studies have shown that Blue Mussels ( Mytilus edulis ) are often an im- 

 portant food item in both North America and in the Old World. 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying The Black Scoter Duck is the last to nest in the Yukon Delta. 

 There, it lays its eggs about the middle of June (Bellrose 1976). Palmer 

 (1976b) indicated that Black Scoters may complete their clutches as early as 

 May in Iceland and that full clutches are commonly present by early June in 

 Iceland and Great Britain. 



Mean Clutch Size Clutches range from about 5 to 8 eggs in Alaska and the 

 British Isles, but apparently are larger in Iceland (Bellrose 1976). Palmer 

 (1976b) indicated that the usual clutch size is 7-8 eggs and considered 6-10 the 

 normal range. The mean of mean clutch sizes for the period 1961-1970 at Lake 

 Myvatyn, Iceland, was 8.7; early nests contained a mean of 8.9 eggs and late 

 nests a mean of 8.1 eggs. Nests considered to be the result of renesting con- 

 tained a mean of 6.1 eggs (Bengtson 1972). 



Incubation Period No information is available on the incubation period 

 of North American Black Scoters. Incubation periods ranging from 26 to 33 days 

 have been reported for Old World Black Scoters (Palmer 1976b). 



Hatching Success For Black Scoters nesting at Lake Myvatyn, Bengtson 

 (1972) indicated that 95.2% of the eggs hatched in nests in which any eggs 

 hatched at all. Bengston estimated a hatching success for Black Scoters of 

 81.8%. Cramp et al. (1977) reported that eggs hatched in 16 of 38 nests in 

 Ireland. There appear to be no adequate data on hatching success for North 

 American Black Scoters. 



Fledging Success No exact information is available. Bengston (1972) 

 estimated that a mean of 2.7 young were produced per female at Lake Myvatn, 

 Iceland. 



Age at Fledging Palmer (1976b) commented that the age of first flight 

 (6-7 weeks) reported by Hantzsch (1905 jLn Palmer 1976b) was only an estimate; 

 Palmer believed that the true age of first flight was greater. Cramp et al. 

 (1977) reported that fledging and independence occur at 45-50 days but they 

 did not indicate the source of their information. 



Age at First Breeding European birds first nest at two years of age 

 (Dement' ev and Gladkov 1967 _in Bellrose 1976). American birds probably do the 

 same (Palmer 1976b). Cramp et al. (1977) stated that age at first breeding is 

 2-3 years. 



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